1. Field of the Invention
The present invention is generally in the field of electrical circuits and systems. More specifically, the present invention is in the field of power management circuits and systems.
2. Background Art
The storage and on-demand delivery of electrical energy is becoming increasingly important due to the ongoing shift from fossil fuel energy sources to environmentally more benign green energy technologies. Electric vehicles and gas/electric hybrid automobiles, for example, utilize arrays of secondary batteries implemented as battery packs that are typically discharged to provide vehicle propulsion and may be charged in response to a vehicle operation such as regenerative braking. The secondary battery packs may constitute a substantial portion of the cost of an electric or gas/electric hybrid vehicle, and their performance, and in particular their longevity, may significantly influence consumer willingness to invest in the initially costlier vehicle.
Energy storage packs, such as the secondary battery packs described above, are commonly assembled from individual batteries, each of which is often assumed or selected to be nominally identical. In practice, however, the batteries, or more generally any other types of energy banks, will have individual performance parameters, such as storage capacity and/or resistance, that vary somewhat from energy bank to energy bank. The distribution or variation among energy banks or batteries may arise, for example, from process variation at the time of manufacturing, from unequal wear during use cycles, and from other non-use related degradation of the energy banks. In general, the distribution of the energy bank variations often becomes wider as the energy banks grow older. Unfortunately, moreover, the longevity and capacity of a group of energy banks used collectively in an energy pack is typically determined by the weakest energy bank in the group. As a result, and in view of the high desirability of extending the lifetime of energy packs such as secondary battery packs, solutions for providing effective energy bank performance management are growing increasingly important.
Conventional approaches to providing management of battery performance, for example, have tended to focus on balancing one aspect of the batteries at a particular time (usually when the battery pack is not in use). At that time, the stronger batteries may be adjusted to a state-of-charge (SOC) corresponding to that of the weakest battery. For example, charge may be transferred from one battery to another (e.g., between adjacent batteries) while the battery pack is offline, until a substantially uniform SOC is achieved. However, in some implementations, it may be costly, inefficient, or otherwise undesirable to take an entire energy pack offline to perform battery management or maintenance operations.
Thus, there is a need to overcome the drawbacks and deficiencies in the art by providing a battery management solution for actively managing secondary batteries or other energy banks during energy transfer, thereby enabling improved performance and increased longevity by a collection of such energy banks implemented as an energy pack.